Step 3 regimens include ABC/3TC/ZDV plus either EFV or TDF. Patients with evidence of treatment-limiting toxicity to Step 3 study drugs have the option of substituting d4T for ZDV, ddI for ABC or TDF, and/or NVP for EFV. Patients with confirmed virologic failure on Step 3 and whose plasma HIV RNA is less than 10,000 copies/ml may either remain on Step 3 or register to Step 4. Patients with two successive plasma HIV RNA levels of 10,000 copies/ml or greater on Step 3 must register to Step 4.